Recovering cellulose ethers from coated paper



Patented Dec. 12, 1939 UNITED STATES RECOVERING CELLULOSE ETHERS FROM COATED PAPER Richard D. Freeman, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Application April 11, 1939, Serial No. 267,316

6 Claims.

This invention relates to a method of recovering cellulose ether films from cellulose ether coated paper broke.

In the process of coating paper with a cellulose derivative solution to provide glossy, soil-proof surfaces,'the paper is conventionally moved in continuous sheet form beneath the source of coating solution as a web of the solution is dropped thereon. The coatingis then dried to remove solvent. It is common to find a ridge or edge trimmed edge bead and the uneven ends which are'cut off from the sheet after breakage, in commen with the sheet from which they are cut, are

coated with valuable cellulose derivative.

Various attempts have been made to recover cellulose derivative coatings from trimmings,

scrap, and other broke obtained as waste-products 2 in paper coating operations. These methods, in

general, have comprised extracting the cellulose derivative away from the paper with the aid of solvents for the cellulose derivative in which the paper itself is insoluble. Such methods require expensive solvents and are defective further in failing to convert the paper fibers to a form which can be reused readily.

It is accordingly among the objects of the invention to provide a method for removing and recovering water-insoluble cellulose ether films from paper which has been coated therewith. It

is another object to provide such a method whereby cellulose ether films can be removed from trimmings, scrap or other broke of cellulose 40 ether-coated paper without the use of extractive solvents for the cellulose ether.

According to the invention, the foregoing objects are attained by heating an aqueous alkaline suspension of cellulose ether-coated paper to a temperature of from 40 to 100 C. and preferably from 80 to 90 C., while agitating the suspension, for from 15 minutes to 4 hours or more until the paper fibers separate from the cellulose ether film. The digested suspension is diluted with water to a consistency of about'0.2 to 1 per cent ofsolids, based on the total Weight of the aqueous suspension. The film of cellulose ether is separated from-the fibers and the film recovered as such by screening the aqueous alkaline slurry on a vibrating screen diaphragm through which the cellulose fibers and water pass freely while the cellulose ether is retained as a film-like deposit.

In a preferred method of carrying out the invention, the paper, coated with cellulose ether, is suspended in a dilute aqueous solution of sodium carbonate, sodium hydroxide, or like alkali, to form a suspension of from 1 to 5 per cent consistency. The solution is heated at a temperature of 80 to 90 C., while being agitated, for a time sufficient to cause the paper to separate from 10 the cellulose ether film and to disintegrate into discrete fibers. The time required varies inversely as the concentration of alkaline material in the aqueous suspension medium and is similarly affected by variation ofthe temperature employed. It has been found satisfactory to'use alkali solutions containing from about 0.2 to 5 per cent of sodium carbonate or sodium hydroxide. After the digestion has been carried out for a period sufiicient to separate the paper fibers from the .20 cellulose ether film, the suspension is diluted with water to produce a readily filterable free-flowing suspension. Suitable filterable consistencies are in the practical range from 0.2 to 1.0 per cent, and preferably about 0.5 per cent of solids based 225 on the total weight of diluted suspension. A preferred means of separating the cellulose ether from the paper fibers, after the alkaline digestion, is to pass the slurry over a vibrating screen diaphragm such as is used in paper making. The 53.0 fibers and water pass through the filter screen and the cellulose ether remains thereon as a crude film which can be lifted orbrushed from the screen and dissolved in the solvent employed in the paper coating operation. The solution is 35 filtered to remove traces of remaining fibers, and after concentration, if necessary, is returned to the paper coating operation. The fibers obtained from the alkaline digestion can be returned to a paper making operation to be re- 40 felted.

The following example illustrates the practice of the invention:

Several samples of a heavy paper stock coated with adherent films of ethyl cellulose, and con- .45 sisting of. parts of paper for each i0 parts of ethyl cellulose, were each suspended in dilute aqueous solutions of sodium carbonate or of sodium hydroxide. The concentration of alkali varied from 0.2 to 5 per cent in the several 'treat- 1 5,0 ing liquors. The suspensions were made up to consistencies varying from 1 to 5 per cent and were heated at to C., while being agitated, until the paper disintegrated into discrete fibers and the cellulose ether was substantially free 65 from adhering fibers. The time required varied from 15 minutes to 2 hours inversely as the concentration of alkali in the digestion liquor. The suspensions of high consistency required more vigorous stirring to effect uniform digestion of the mass and separation of the fibers from the cellulose ether than did suspensions of 3 per cent consistency or less. After digestion and disintegration of the paper into a pulpy fibrous mass, the various suspensions were diluted with water to about 0.5 per cent consistency. The samples were each poured over a vibrating screen diaphragm and the ethyl cellulose recovered in a substantially fiber-free state. The crude films of ethyl cellulose were dissolved in cellulose ether solvents, the solutions were filtered to remove traces of fibers, and then returned to the reservoir of ethyl cellulose solution used to coat paper. The amount of ethyl cellulose recovered from the paper in form suitable for reuse was from 95 to 98 per cent of that known to have been present in the coating on the paper scraps being treated. The recovery of paper fibers, free from any detectable trace of ethyl cellulose, was from 83 to 90 per cent of the weight of paper present, losses being due to handling and to rosin sizing in the paper which was destroyed by the alkaline digestion.

The recovered ethyl cellulose could be cast into useful films having tensile strengths near 400 kilograms per square centimeter and capable of from 25 to 35 per cent elongation.

The example has illustrated the recovery of water-insoluble ethyl cellulose from paper coated therewith. The method is equally applicable to the recovery of other cellulose ethers which are insoluble in water and in dilute aqueous alkali at the digestion temperature employed. Examples of such ethers include lauryl ethyl cellulose, propyl cellulose, ethyl butyl cellulose, benzyl cellulose, ethyl benayl cellulose, methyl ethyl cellulose, and methyl cellulose containing 2 or more methyl groups per unit. If cellulose ethers are to be recovered which ordinarily dissolve in cold water, but which are insoluble in hot water, the operation may be carried out at a temperature at which the cellulose ether is insoluble in water or in dilute alkali.

The practical temperature range for carrying out the digestion has been given as 40 to 100 C., and the preferred range as 80 to 90 C. It is to be understood that temperatures from room temperature to 40 C. may be employed but that the time required is unduly long. Similarly, temperatures above 100 C. may be employed under suitable super-atmospheric pressure.

It must be understood that no precise limits can be set for the amount of alkali in the digestion liquor, but that water alone is not effective on a comparable basis-and that concentrations of alkali greater than about per cent are uneconomical in that they produce no improved result. The range of working consistencies is given only as a practical range, lower or higher consistencies being operative though probably uneconomical. If the consistency is too low, inordinately large volumes of digestion liquor must be handled, while with high consistencies, in the range from 5 to per cent, too much power is required to provide thorough and efiicient agitation.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the method herein disclosed, provided the steps stated by any of the following claims or the equivalent of such stated steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a method for the recovery of cellulose ethers from paper coated therewith, the steps which consist in digesting the coated paper with a dilute aqueous solution of an alkali, while agitating the mixture at a temperature at which the cellulose ether is insoluble in the dilute alkaline solution, until the paper is disintegrated into discrete fibers, and separating the cellulose ether from the slurry of cellulose fibers.

2. In a method for the recovery of waterinsoluble cellulose ethers from paper coated therewith, the steps which consist in digesting the coated paper with an aqueous alkali solution of from 0.2 to 5 per cent concentration, while agitating the mixture at a temperature from 40 to 100 C., for a period in the range from minutes to 4 hours until the paper is disinte rated into discrete fibers, diluting the digested mixture to a solids consistency of from 0.2 to 1 per cent, and separating the cellulose ether from the dilute slurry of cellulose fibers.

3. In a method for the recovery of waterinsoluble cellulose ethers from paper coated therewith, the steps which consist in digesting the coated paper at a solids consistency of from i to 5 per cent with an aqueous alkali solution of from 0.2 to 5 per cent concentration, while agitating the mixture at a temperature from 40 to 100 C., until the paper is disintegrated into discrete fibers, diluting the digested mixture to a solids consistency of from 0.2 to l per cent, and passing the dilute slurry over a vibrating screen diaphragm, thereby to separate the cellulose ether from the aqueous slurry of cellulose fibers.

4. In a method for the recovery of waterinsoluble cellulose ethers from paper coated therewith, the steps which consist in digesting the coated paper at a solids consistency of about 2 per cent with a l to 5 per cent aqueous solution of sodium carbonate, while agitating the mixture at a temperature from 80 to 90 C., until the paper is disintegrated into discrete fibers, diluting the digested mixture to a solids consistency of about 0.5 per cent, and passing the dilute slurry over a vibrating screen diaphragm, thereby to separate the cellulose ether from the aqueous slurry of cellulose fibers.

5. In a method for the recovery of cellulose ethers from paper coated therewith, the steps which consist in digesting the coated paper with a dilute aqueous solution of an alkali, while agitating the mixture at a temperature at which the cellulose ether is insoluble in the dilute alkaline solution, until the paper is disintegrated into discrete fibers, diluting the digested mixture to a solids consistency of from 0.2 to 1 per cent, separating the cellulose ether from the dilute slurry of cellulose fibers, dissolving the separated cellulose ether in a volatile organic solvent, and filtering the solution to remove final traces of cellulose fibers and to provide a clear cellulose ether solution.

6. The method according to claim 1, wherein the cellulose ether is water-insoluble ethyl cellulose.

RICHARD D. FREEMAN. 

